Kansai prepares Mihama 3 for 60 years of operation

08 June 2017

Kansai Electric Power Company has decided to operate unit 3 of the Mihama nuclear power plant in Japan's Fukui Prefecture beyond 40 years. The company has drawn up a plan for safety improvement works at the unit, which has already received regulatory approval to operate for a further 20 years.

Kansai's three Mihama units (Image: NRA)

Under revised regulations which came into force in July 2013, Japanese reactors have a nominal operating period of 40 years. Extensions can be granted once only and limited to a maximum of 20 years, contingent on exacting safety requirements.

In November 2016, Japan's Nuclear Regulation Authority (NRA) approved an extension to the operating period for Kansai Electric Power's Mihama unit 3.

The NRA's decision cleared the 780 MWe pressurised water reactor to operate until 2036. It had previously been licensed until last year. Mihama 3 is the third Japanese unit to be granted a licence extension enabling it to operate beyond 40 years under the revised regulations, following Kansai's Takahama 1 and 2 which received NRA approval last June.

Kansai announced today it had made the official decision to operate the unit beyond 40 years. It also released a schedule for safety improvement work it will carry out at the unit to enable it operate for an additional 20 years.

Most of the work is related to improving the unit's seismic resistance and carrying out preventative maintenance. Kansai plans to reinforce the used fuel pool and replace its fuel assembly rack. It will also replace the internal structure of the reactor core and improve the seismic resistance of the reactor containment vessel. The unit's central control panel is also to be replaced.

Other work includes improving fire protection work, including replacing old cables with fire-resistant cabling, installing fire protection panels and fire detectors, as well as installing new fire extinguishing equipment. A new, higher tidal barrier will also be constructed at the plant.

Kansai said it will "proceed with implementation of the work plan to allow for operation for 60 years which was compiled today placing the top priority on safety". The company aims to complete the work by the end of January 2020.

Since May 2015, Mihama 3 has undergone special inspections and evaluations to assess the effects of aging management technology, and a long-term maintenance management policy has been drawn up for the plant. Kansai submitted its application to extend the unit's operating period in November 2015. The company submitted a subsequent amendment to the application to include its evaluation of the unit's earthquake resistance.

The NRA has also approved Kansai's revised nuclear facility safety policy concerning countermeasures for deterioration due to aging, which was submitted to the regulator at the same time as the operating period extension application.

Mihama 3 entered commercial operation in 1976, but remains offline following the 2011 Fukushima accident. The NRA has approved Kansai's plans to upgrade the plant, for which it submitted a restart application in March 2015.